A wall is 7 m wide and 3 m high, and contains two doors and one window. Details onthe wall components are as follows:• The window is a triple-glazed glass window with a 6.4 mm space filled withargon gas. The window surfaces do not have any special surface emissivitycoatings. The window dimensions are 2 m by 1 m, and the window has analuminum sash with a thermal break.• The wall material has an overall heat-transfer coefficient of 0.5 W/(m2-ºC).• Each door is a solid core flush door made of wood, with a thickness of 4.5 cm.Also, each door is 2.1 m high and 0.8 m wide. Both doors are accompanied bymetal storm doors.a) Determine the overall heat-transfer coefficient [in W/(m2-ºC)] for the wallcombination (based on the overall dimensions of the wall-window-doorscombination), assuming winter conditions.b) The room is maintained at a temperature of 22ºC. If the heat flow rate through thewall is 0.4 kW at a certain time, what is the outdoor temperature at that time?Infiltration can be neglected.

A wall is 7 m wide and 3 m high, and contains two doors and one window. Details onthe wall components are as follows:• The window is a triple-glazed glass window with a 6.4 mm space filled withargon gas. The window surfaces do not have any special surface emissivitycoatings. The window dimensions are 2 m by 1 m, and the window has analuminum sash with a thermal break.• The wall material has an overall heat-transfer coefficient of 0.5 W/(m2-ºC).• Each door is a solid core flush door made of wood, with a thickness of 4.5 cm.Also, each door is 2.1 m high and 0.8 m wide. Both doors are accompanied bymetal storm doors.a) Determine the overall heat-transfer coefficient [in W/(m2-ºC)] for the wallcombination (based on the overall dimensions of the wall-window-doorscombination), assuming winter conditions.b) The room is maintained at a temperature of 22ºC. If the heat flow rate through thewall is 0.4 kW at a certain time, what is the outdoor temperature at that time?Infiltration can be neglected.

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter8: Natural Convection

Section: Chapter Questions

Problem 8.44P

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1.25 A spherical vessel, 0.3 m in diameter, is located in a large room whose walls are at 27°C (see sketch). If the vessel is used to store liquid oxygen at –183°C and both the surface of the storage vessel and the walls of the room are black, calculate the rate of heat transfer by radiation to the liquid oxygen in watts and in Btu/h.
8.15 A mercury bath at is to be heated by immersing cylindrical electric heating rods, each 20 cm tall and 2 cm in diameter. Calculate the maximum electric power rating of a typical rod if its maximum surface temperature is .
Determine the power requirement of a soldering iron in which the tip is maintained at 400C. The tip is a cylinder 3 mm in diameter and 10 mm long. The surrounding air temperature is 20C, and the average convection heat transfer coefficient over the tip is 20W/m2K. The tip is highly polished initially, giving it a very low emittance.
Liquefied natural gas (LNG) is transported around the globe using ships similar to thatshown in Figure QA3. This ship has four pressurised cylindrical steel tanks each ofradius of 20 m. The tanks are internally insulated with 30 cm of polyurethane foamwhich keeps the LNG at a constant -162 ºC. Take the effective sky temperature is 265K and the net radiative thermal energy exchange with the sky as 1x10^6 W. (a) Calculate the surface temperature of the end (facing the sun) of a tank.(b) Calculate the conductive heat transfer through the end (facing the sun)of a tank. DATA FOR QUESTION: Thermal conductivity, polyurethane foam = 0.02 W/mKStefan’s Constant = 5.67x10^-8 W/m^2K^4Emissivity, steel = 0.95 answers: a) 375K b) 22.1kW
Liquefied natural gas (LNG) is transported around the globe using ships similar to thatshown in Figure QA3. This ship has four pressurised cylindrical steel tanks each ofradius of 20 m. The tanks are internally insulated with 30 cm of polyurethane foamwhich keeps the LNG at a constant -162 ºC. Take the effective sky temperature is 265K and the net radiative thermal energy exchange with the sky as 1x106 W. Calculate the surface temperature of the end (facing the sun) of a tank. Calculate the conductive heat transfer through the end (facing the sun)of a tank.
Liquefied natural gas (LNG) is transported around the globe using ships similar to thatshown in Figure QA3. This ship has four pressurised cylindrical steel tanks each ofradius of 20 m. The tanks are internally insulated with 30 cm of polyurethane foamwhich keeps the LNG at a constant -162 ºC. Take the effective sky temperature is 265K and the net radiative thermal energy exchange with the sky as 1x10^6 W. (a) Calculate the surface temperature of the end (facing the sun) of a tank.(b) Calculate the conductive heat transfer through the end (facing the sun)of a tank. answers: a) 375K b) 22.1kW
A 3x3m plate at 500 degC is suspended vertically in a very large room. The plate has an emissivity of 0.13, The room is at 25degC. What is the net heat transfer from the plate?
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